I don't know what to call these images, but they're very often used in the image processing world as standard examples to show the output of a particular operation. Here's a link to the page describing Lena as a "standard test image". Are there similar canonical audio clips used to demonstrate the effects of certain audio filters or operations?
The closest example I can think of is the beginning of Suzanne Vega's "Tom's Diner" which has been used for the mpeg-1 layer 3 development, and is still occasionally used to demo audio codecs.
Audio processing is a large field, but specifically in speech processing, an open database of samples known as Harvard Sentences is widely used. Harvard sentences are phonetically balanced collections of sentences in American English. Many equivalent databases exist for other languages as well.
Actual files with Harvard Sentences speech can be found here.
I also think that NIST database is very popular when it comes to speech recognition tasks. In fact it is a standard for comparison of new algorithms and techniques during yearly challenges.
load handel containing snippet of G.F.Handel - Hallelujah is quite commonly used.
The European Broadcasting Union's (EBU) Sound Quality Assessment Material (SQAM) resource is pretty popular. https://tech.ebu.ch/publications/sqamcd
Do not underestimate the power of 1 kHz sine wave at 0 dBFS. In mono. A lot of things that are wrong with signal paths can be found with that.
I've built and calibrated enough audio systems that I can whistle 1 kHz pretty exactly. From simple memory.
Other than that, I.G.Y by Donald Fagen is so popular as test track that it's been forbidden by a number of festivals.